Command & Conquer: Generals is a real-time strategy video game and the seventh installment in the Command & Conquer series. It was released for Microsoft Windows and Mac OS operating systems in 2003 and 2004. While the Windows version of Generals was developed by EA Pacific and published by EA Games, the Mac OS X version was developed and published by Aspyr Media. The Mac OS X version was re-released by Aspyr for the Mac App Store on March 12, 2015. In the game, the player can choose from three different factions: the United States, China and the Global Liberation Army (GLA). Generals utilizes SAGE (Strategy Action Game Engine), an extended version of the Command & Conquer: Renegade's 3D engine. An expansion pack, entitled Command & Conquer: Generals – Zero Hour, was additionally released for PC in 2003, and for Mac OS in 2005. Both Generals and Zero Hour were met with highly positive reviews. A sequel, Command & Conquer: Generals 2, was in development, until it was repurposed to a free-to-play game known as simply Command & Conquer. The new game was part of the Generals franchise and was cancelled on October 29, 2013 by EA after negative feedback during the closed alpha test. Zero Hour also contains 3 new campaigns of five missions each, one for each side, with their chronological order being USA first, GLA second, and China last. Unlike the previous campaigns, which were noted by Command and Conquer fans for not having full motion video cinematic sequences during mission briefing, the Zero Hour campaigns return to that Command and Conquer tradition, each showing a live-action video of a news reporter of the respective side giving details about the situation behind the current mission. The plot behind the Zero Hour campaigns picks up where it left off at the end of the previous campaigns.